I think the length depends on the type of website. For regular companies, community sites, and Internet memes having a longer name is OK. But whenever I try to think up a domain name for an Internet startup I try to keep it down to 2-3 syllables. If you look at the most successful consumer facing start ups, they may not all have 6 characters or less, but probably 95% do have only 2 syllables, or at least only 2 stressed syllables. Character length doesn't matter as much on the Internet because most people are clicking on links or copying+pasting, but having only a few syllables makes the name easier to say in conversation or when thinking to yourself.
I agree with what most other people have said here about doing it in your spare time and then going in full time when you know what you're doing. Give full time effort when the business requires your full time effort, there's no point in doing it full time when you have no users and no application to support.
Books I recommend: Rework, Lucky or Smart, The Art of the Start
Languages: HTML, CSS, and Javascript are a must (jQuery is a great JS library to use). I recommend Python and Django for the server side, though what ever language you choose you should use an MVC framework (Django, Rails, CakePHP).